Fixes:
- Don't show 'Configure banners' link if already in an ICarouselFolder

Ideas:
- Support rich text as an alternative to image
- Add 'position indicator' and pause button
- Add settings to Carousel folders (via a schema extender)
  - Delay
  - Defaults from global configlet
- Configlet option for which viewlet manager it is rendered in
- Validate image size
